DESCRIPTION

GNUas is really a family of assemblers. If you use (or have used) the GNU assembler on one architecture, you should find a fairly similar environment when you use it on another architecture. Each version has much in common with the others, including object file formats, most assembler directives (often called pseudo-ops) and assembler syntax.

as is primarily intended to assemble the output of the GNU C compiler "gcc" for use by the linker "ld". Nevertheless, we’ve tried to make as assemble correctly everything that other assemblers for the same machine would assemble. Any exceptions are documented explicitly. This doesn’t mean as always uses the same syntax as another assembler for the same architecture; for example, we know of several incompatible versions of 680x0 assembly language syntax.

Each time you run as it assembles exactly one source program. The source program is made up of one or more files. (The standard input is also a file.)

You give as a command line that has zero or more input file names. The input files are read (from left file name to right). A command line argument (in any position) that has no special meaning is taken to be an input file name.

If you give as no file names it attempts to read one input file from the as standard input, which is normally your terminal. You may have to type ctl-D to tell as there is no more program to assemble.

Use −− if you need to explicitly name the standard input file in your command line.

If the source is empty, as produces a small, empty object file.

as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs as automatically. Warnings report an assumption made so that as could keep assembling a flawed program; errors report a grave problem that stops the assembly.

If you are invoking as via the GNU C compiler, you can use the −Wa option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the −Wa) by commas. For example:

gcc -c -g -O -Wa,-alh,-L file.c

This passes two options to the assembler: −alh (emit a listing to standard output with high-level and assembly source) and −L (retain local symbols in the symbol table).

Usually you do not need to use this −Wa mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the GNU compiler driver with the −v option to see precisely what options it passes to each compilation pass, including the assembler.)

OPTIONS

@file

Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed.

Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.

−a[cdhlmns]

Turn on listings, in any of a variety of ways:

−ac

omit false conditionals

−ad

omit debugging directives

−ah

include high-level source

−al

include assembly

−am

include macro expansions

−an

omit forms processing

−as

include symbols

=file

set the name of the listing file

You may combine these options; for example, use −aln for assembly listing without forms processing. The =file option, if used, must be the last one. By itself, −a defaults to −ahls.

−−alternate

Begin in alternate macro mode.

−D

Ignored. This option is accepted for script compatibility with calls to other assemblers.

−−defsymsym=value

Define the symbol sym to be value before assembling the input file. value must be an integer constant. As in C, a leading 0x indicates a hexadecimal value, and a leading 0 indicates an octal value.

Generate debugging information for each assembler source line using whichever debug format is preferred by the target. This currently means either STABS , ECOFF or DWARF2 .

−−gstabs

Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it.

−−gstabs+

Generate stabs debugging information for each assembler line, with GNU extensions that probably only gdb can handle, and that could make other debuggers crash or refuse to read your program. This may help debugging assembler code. Currently the only GNU extension is the location of the current working directory at assembling time.

−−gdwarf−2

Generate DWARF2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it. Note−−−this option is only supported by some targets, not all of them.

−−help

Print a summary of the command line options and exit.

−−target−help

Print a summary of all target specific options and exit.

−Idir

Add directory dir to the search list for ".include" directives.

−J

Don’t warn about signed overflow.

−K

Issue warnings when difference tables altered for long displacements.

−L

−−keep−locals

Keep (in the symbol table) local symbols. These symbols start with system-specific local label prefixes, typically .L for ELF systems or L for traditional a.out systems.

−−listing−lhs−width=number

Set the maximum width, in words, of the output data column for an assembler listing to number.

−−listing−lhs−width2=number

Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to number.

−−listing−rhs−width=number

Set the maximum width of an input source line, as displayed in a listing, to number bytes.

−−listing−cont−lines=number

Set the maximum number of lines printed in a listing for a single line of input to number + 1.

−oobjfile

Name the object-file output from asobjfile.

−R

Fold the data section into the text section.

Set the default size of GAS ’s hash tables to a prime number close to number. Increasing this value can reduce the length of time it takes the assembler to perform its tasks, at the expense of increasing the assembler’s memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed.

−−reduce−memory−overheads

This option reduces GAS ’s memory requirements, at the expense of making the assembly processes slower. Currently this switch is a synonym for −−hash−size=4051, but in the future it may have other effects as well.

−−statistics

Print the maximum space (in bytes) and total time (in seconds) used by assembly.

−−strip−local−absolute

Remove local absolute symbols from the outgoing symbol table.

−v

−version

Print the as version.

−−version

Print the as version and exit.

−W

−−no−warn

Suppress warning messages.

−−fatal−warnings

Treat warnings as errors.

−−warn

Don’t suppress warning messages or treat them as errors.

−w

Ignored.

−x

Ignored.

−Z

Generate an object file even after errors.

−− ⎪files...

Standard input, or source files to assemble.

The following options are available when as is configured for an ARC processor.
−marc[5⎪6⎪7⎪8]

This option selects the core processor variant.

−EB ⎪ −EL

Select either big-endian (−EB) or little-endian (−EL) output.

The following options are available when as is configured for the ARM processor family.
−mcpu=processor[+extension...]

Specify which ARM processor variant is the target.

−march=architecture[+extension...]

Specify which ARM architecture variant is used by the target.

−mfpu=floating-point-format

Select which Floating Point architecture is the target.

−mfloat−abi=abi

Select which floating point ABI is in use.

−mthumb

Enable Thumb only instruction decoding.

−mapcs−32 ⎪ −mapcs−26 ⎪ −mapcs−float ⎪ −mapcs−reentrant

Select which procedure calling convention is in use.

−EB ⎪ −EL

Select either big-endian (−EB) or little-endian (−EL) output.

−mthumb−interwork

Specify that the code has been generated with interworking between Thumb and ARM code in mind.

−k

Specify that PIC code has been generated.

See the info pages for documentation of the CRIS-specific options.

The following options are available when as is configured for a D10V processor.

−O

Optimize output by parallelizing instructions.

The following options are available when as is configured for a D30V processor.

−O

Optimize output by parallelizing instructions.

−n

Warn when nops are generated.

−N

Warn when a nop after a 32−bit multiply instruction is generated.

The following options are available when as is configured for the Intel 80960 processor.
−ACA ⎪ −ACA_A ⎪ −ACB ⎪ −ACC ⎪ −AKA ⎪ −AKB ⎪ −AKC ⎪ −AMC

Specify which variant of the 960 architecture is the target.

−b

Add code to collect statistics about branches taken.

−no−relax

Do not alter compare-and-branch instructions for long displacements; error if necessary.

The following options are available when as is configured for the Ubicom IP2K series.
−mip2022ext

Specifies that the extended IP2022 instructions are allowed.

−mip2022

Restores the default behaviour, which restricts the permitted instructions to just the basic IP2022 ones.

The following options are available when as is configured for the Renesas M32C and M16C processors.
−m32c

Assemble M32C instructions.

−m16c

Assemble M16C instructions (the default).

The following options are available when as is configured for the Renesas M32R (formerly Mitsubishi M32R) series.
−−m32rx

Specify which processor in the M32R family is the target. The default is normally the M32R, but this option changes it to the M32RX.

Specify what processor in the 68000 family is the target. The default is normally the 68020, but this can be changed at configuration time.

−m68881 ⎪ −m68882 ⎪ −mno−68881 ⎪ −mno−68882

The target machine does (or does not) have a floating-point coprocessor. The default is to assume a coprocessor for 68020, 68030, and cpu32. Although the basic 68000 is not compatible with the 68881, a combination of the two can be specified, since it’s possible to do emulation of the coprocessor instructions with the main processor.

−m68851 ⎪ −mno−68851

The target machine does (or does not) have a memory-management unit coprocessor. The default is to assume an MMU for 68020 and up.

For details about the PDP−11 machine dependent features options, see PDP−11−Options.
−mpic ⎪ −mno−pic

Redirect error output to a file, for broken systems which don’t support such behaviour in the shell.

The following options are available when as is configured for a MIPS processor.
−Gnum

This option sets the largest size of an object that can be referenced implicitly with the "gp" register. It is only accepted for targets that use ECOFF format, such as a DECstation running Ultrix. The default value is 8.

Generate code for a particular MIPS Instruction Set Architecture level. −mips1 is an alias for −march=r3000, −mips2 is an alias for −march=r6000, −mips3 is an alias for −march=r4000 and −mips4 is an alias for −march=r8000. −mips5, −mips32, −mips32r2, −mips64, and −mips64r2 correspond to generic MIPS V, MIPS32 , MIPS32 Release 2, MIPS64 , and MIPS64 Release 2ISA processors, respectively.

−march=CPU

Generate code for a particular MIPS cpu.

−mtune=cpu

Schedule and tune for a particular MIPS cpu.

−mfix7000
−mno−fix7000

Cause nops to be inserted if the read of the destination register of an mfhi or mflo instruction occurs in the following two instructions.

The register sizes are normally inferred from the ISA and ABI , but these flags force a certain group of registers to be treated as 32 bits wide at all times. −mgp32 controls the size of general-purpose registers and −mfp32 controls the size of floating-point registers.

−mips16
−no−mips16

Generate code for the MIPS 16 processor. This is equivalent to putting ".set mips16" at the start of the assembly file. −no−mips16 turns off this option.

−msmartmips
−mno−smartmips

Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent to putting ".set smartmips" at the start of the assembly file. −mno−smartmips turns off this option.

−mips3d
−no−mips3d

Generate code for the MIPS−3D Application Specific Extension. This tells the assembler to accept MIPS−3D instructions. −no−mips3d turns off this option.

−mdmx
−no−mdmx

Generate code for the MDMX Application Specific Extension. This tells the assembler to accept MDMX instructions. −no−mdmx turns off this option.

−mdsp
−mno−dsp

Generate code for the DSP Application Specific Extension. This tells the assembler to accept DSP instructions. −mno−dsp turns off this option.

−mmt
−mno−mt

Generate code for the MT Application Specific Extension. This tells the assembler to accept MT instructions. −mno−mt turns off this option.

−−construct−floats
−−no−construct−floats

The −−no−construct−floats option disables the construction of double width floating point constants by loading the two halves of the value into the two single width floating point registers that make up the double width register. By default −−construct−floats is selected, allowing construction of these floating point constants.

−−emulation=name

This option causes as to emulate as configured for some other target, in all respects, including output format (choosing between ELF and ECOFF only), handling of pseudo-opcodes which may generate debugging information or store symbol table information, and default endianness. The available configuration names are: mipsecoff, mipself, mipslecoff, mipsbecoff, mipslelf, mipsbelf. The first two do not alter the default endianness from that of the primary target for which the assembler was configured; the others change the default to little− or big-endian as indicated by the b or l in the name. Using −EB or −EL will override the endianness selection in any case.

This option is currently supported only when the primary target as is configured for is a MIPS ELF or ECOFF target. Furthermore, the primary target or others specified with −−enable−targets=... at configuration time must include support for the other format, if both are to be available. For example, the Irix 5 configuration includes support for both.

Eventually, this option will support more configurations, with more fine-grained control over the assembler’s behavior, and will be supported for more processors.

−nocpp

as ignores this option. It is accepted for compatibility with the native tools.

−−trap
−−no−trap
−−break
−−no−break

Control how to deal with multiplication overflow and division by zero. −−trap or −−no−break (which are synonyms) take a trap exception (and only work for Instruction Set Architecture level 2 and higher); −−break or −−no−trap (also synonyms, and the default) take a break exception.

−n

When this option is used, as will issue a warning every time it generates a nop instruction from a macro.

The following options are available when as is configured for an MCore processor.
−jsri2bsr
−nojsri2bsr

Enable or disable the JSRI to BSR transformation. By default this is enabled. The command line option −nojsri2bsr can be used to disable it.

−sifilter
−nosifilter

Enable or disable the silicon filter behaviour. By default this is disabled. The default can be overridden by the −sifilter command line option.

−relax

Alter jump instructions for long displacements.

−mcpu=[210⎪340]

Select the cpu type on the target hardware. This controls which instructions can be assembled.

−EB

Assemble for a big endian target.

−EL

Assemble for a little endian target.

See the info pages for documentation of the MMIX-specific options.

The following options are available when as is configured for an Xtensa processor.
−−text−section−literals ⎪ −−no−text−section−literals

With −−text−section−literals, literal pools are interspersed in the text section. The default is −−no−text−section−literals, which places literals in a separate section in the output file. These options only affect literals referenced via PC-relative "L32R" instructions; literals for absolute mode "L32R" instructions are handled separately.

−−absolute−literals ⎪ −−no−absolute−literals

Indicate to the assembler whether "L32R" instructions use absolute or PC-relative addressing. The default is to assume absolute addressing if the Xtensa processor includes the absolute "L32R" addressing option. Otherwise, only the PC-relative "L32R" mode can be used.

−−target−align ⎪ −−no−target−align

Enable or disable automatic alignment to reduce branch penalties at the expense of some code density. The default is −−target−align.

−−longcalls ⎪ −−no−longcalls

Enable or disable transformation of call instructions to allow calls across a greater range of addresses. The default is −−no−longcalls.

−−transform ⎪ −−no−transform

Enable or disable all assembler transformations of Xtensa instructions. The default is −−transform; −−no−transform should be used only in the rare cases when the instructions must be exactly as specified in the assembly source.

The following options are available when as is configured for a Z80 family processor.
−z80

Assemble for Z80 processor.

−r800

Assemble for R800 processor.

−ignore−undocumented−instructions
−Wnud

Assemble undocumented Z80 instructions that also work on R800 without warning.

−ignore−unportable−instructions
−Wnup

Assemble all undocumented Z80 instructions without warning.

−warn−undocumented−instructions
−Wud

Issue a warning for undocumented Z80 instructions that also work on R800.

−warn−unportable−instructions
−Wup

Issue a warning for undocumented Z80 instructions that do not work on R800.

−forbid−undocumented−instructions
−Fud

Treat all undocumented instructions as errors.

−forbid−unportable−instructions
−Fup

Treat undocumented Z80 instructions that do not work on R800 as errors.

SEE ALSO

COPYRIGHT

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled " GNU Free Documentation License".